Monday Aug. 30, 2010
click here to download today's notes in a more printer friendly format

Music today was from Amadou and Mariam.  We had time for 3 songs: Beaux Dimanches, Sabali, and Ce N'est pas Bon.

Carbon monoxide is a serious hazard indoors where is can build to much higher levels than would ever be found outdoors.  You may remember having heard about an incident at the beginning of the school year in 2007.  Carbon monoxide from a malfunctioning hot water heater sickened 23 Virginia Tech students in an apartment complex.  The CO concentration is thought to have reached 500 ppm.  You can get an idea of what kinds of health effects concentrations this high could cause from the figure. on p. 9 in the photocopied ClassNotes.


The 400 ppm line in the ClassNotes approaches the level where CO would cause coma and death.  At Virginia Tech several students were found unconscious and one or two had stopped breathing but they were revived.

Carbon monoxide alarms are relatively inexpensive (~$50) and readily available at a hardware store.  They will monitor CO concentrations indoors and warn you when concentrations reach hazardous levels. Indoors CO is produced by gas furnaces and water heaters that are either operating improperly or aren't being adequately vented to the outdoors.  A few hundred people are killed indoors by carbon monoxide every year in the United States.  You can learn more about carbon monoxide hazards and risk prevention at the Consumer Product Safety Commission web page.

Here's a figure I mentioned, but didn't cover in class.  This is an example of a habit I have of "beating some concepts to death."  The rather busy picture below illustrates how small changes in how air temperature changes with increasing altitude can determine whether the atmosphere will be stable or unstable.   Just for the purposes of illustration imagine riding a bicycle north from Swan and River Rd up the hill to Swan and Sunrise (fhe figure shows an elevation change of 1000 ft, it is actually quite a bit less than that). 



At far left the air temperature goes from 47o F to 41o F, a drop of 6o F.  This is a fairly rapid rate of decrease with increasing altitude and would make the atmosphere absolutely unstable.  The atmosphere wouldn't remain this way.  Air at the ground would rise, air higher up would sink, and the temperature profile would change (the rate of decrease with increasing altitude would lessen).  In some ways it would be like trying to pour vinegar on top of oil in a glass.  The lower density oil would rise because it would "want" to float on top of the higher density vinegar.

The next picture shows air temperature decreasing a little more slowly with increasing altitude.  This small change makes the atmosphere conditionally unstable (we won't go into what the conditions might be).  The atmosphere is often in this state. 

The atmosphere cools only 2o F in 1000 feet in the next picture.  This creates an absolutely stable atmosphere.  Air at the ground will remain at the ground and won't rise and mix with air higher up.  Compare this with the glass containing vinegar and a layer of oil on top.  The two layers won't mix.

Air temperature in the last figure actually increases with increasing altitude.  This is a temperature inversion and is very common on winter mornings.  The atmosphere is extremely stable under these conditions. 

Temperature inversions are something you can check out for yourself later this semester.  Head north on Swan Rd. on your bicycle early some winter morning.  You will pass through some pretty cold air as you cross the Rillito River.  By the time you get to Sunrise, the air can be 10 to 15 degrees warmer and will seem balmy compared to the cold air at the bottom of the hill.  If you're up for a real hill-climbing challenge continue north on Swan past Skyline.  You'll find a short but very steep section of road at the far north end of Swan.

As long as we're talking about bicycles and hills here's a picture of my bicycle.  I was in France in July 2009 trying to ride up some of the famous Tour de France mountain stages in the Alps.  One of the most famous is the Alpe d'Huez.  That's my bicycle, a green "Gilmour" (Andy Gilmour is a local bicycle builder) at the top of the Alpe d'Huez.



The next picture shows the last 3 or 4 km of the road to the summit of Mt. Ventoux, another famous climb in Provence.  I was there just a few weeks ago.


Next in our coverage of air pollutants is tropospheric ozone and photochemical smog (aka Los Angeles type smog)



The figure above can be found on p. 14a in the photocopied ClassNotes.  Ozone has a Dr. Jekyll (good) and Mr. Hyde (bad) personality.  Ozone in the stratosphere (the ozone layer) is beneficial, it absorbs dangerous high energy ultraviolet light (which would otherwise reach the ground and cause skin cancer, cataracts, and many other problems).

Ozone in the troposphere is bad, it is a pollutant.  This is the stuff we will first be concerned with today.  Tropospheric ozone is a key component of photochemical smog (also known as Los Angeles-type smog)

We'll be making some photochemical smog as a class demonstration.  This will require ozone (and a hydrocarbon of some kind).  We'll use the simple stratospheric recipe for making ozone in the demonstration rather than the more complex tropospheric process (4-step process shown below).




At the top of this figure you see that a more complex series of reactions is responsible for the production of tropospheric ozone.  The production of tropospheric ozone begins with nitric oxide (NO).  NO is produced when nitrogen and oxygen in air are heated (in an automobile engine for example) and react.  The NO can then react with oxygen to make nitrogen dioxide, the poisonous brown-colored gas I decided not to make in class.  Sunlight can dissociate (split) the nitrogen dioxide molecule producing atomic oxygen (O) and NO.  O and O2 react in a 4th step to make ozone (O3).  Because ozone does not come directly from an automobile tailpipe or factory chimney, but only shows up after a series of reactions, it is a secondary pollutant.   Nitric oxide would be the primary pollutant in this example.

NO is produced early in the day (during the morning rush hour).  The concentration of NO2 peaks somewhat later.  Because sunlight is needed in one of the reactions and because peak sunlight normally occurs at noon, the highest ozone concentrations are usually found in the afternoon.  Ozone concentrations are also usually higher in the summer when the sunlight is most intense.



Once ozone is formed, the ozone can react with a hydrocarbon of some kind to make a product gas.  The ozone, hydrocarbon, and product gas are all invisible, but the product gas sometimes condenses to make a visible smog cloud or haze.  The cloud is composed of very small droplets or solid particles.  They're too small to be seen but they are able to scatter light - that's why you can see the cloud.

Here's a pictorial summary of the photochemical smog demonstration.


Once the cloud had formed we shined the laser beam through the flask.  Laser light wasn't visible to the left or the right of the flask, only in the flask where smog droplets were present and scattering laser light.  The smog droplets (and they may well be solid particles, I don't know) are very small and even the weakest air current is able to keep them suspended.

Next we moved on to the 3rd air pollutant that we will be discussing - sulfur dioxide.  Here's some basic information from the left hand of p. 11 in the photocopied ClassNotes.

Sulfur dioxide is produced by the combustion of sulfur containing fuels such as coal.  Combustion of fuel also produces carbon dioxide and carbon monoxide.  People probably first became aware of sulfur dioxide because it has an unpleasant smell.  Carbon dioxide and carbon monoxide are odorless.  That is why sulfur dioxide was the first pollutant people became aware of.

Volcanoes are a natural source of sulfur dioxide.





The Great London smog is still one of the two or three deadliest air pollution events in history.
Because of a subsidence inversion the atmosphere was stable
SO2 emitted into air at ground level couldn't mix with cleaner air above. 
The SO2 concentration was able to build to dangerous levels. 

4000 people died during this 4 or 5 day period. 
As many as 8000 additional people died in the following weeks and months. 
Some of the photographs below come from articles published in 2002 on the 50th anniversary of the event. 
 


from:
http://news.bbc.co.uk/1/hi/uk/2542315.stm

from:
http://news.bbc.co.uk/1/hi/health/2545747.stm

from:
http://news.bbc.co.uk/1/hi/england/2543875.stm

from:
http://www.npr.org/templates/story/story.php?storyId=873954

The sulfur dioxide didn't kill people directly.   
The SO2 aggravated an existing condition of some kind and hastened their death. 
The SO2 probably also made people susceptible to bacterial infections such as pneumonia.
This link discusses the event and its health effects in more detail.

Note:
London type smog which contains sulfur dioxide and is most common during the winter is very different from photochemical or Los Angeles type smog.  Los Angeles type smog contains ozone and is most common in the summer.

Some other air pollution disasters also involved high SO2 concentrations. 
One of the deadliest events in the US occurred in 1948 in Donora, Pennsylvania.



"This eerie photograph was taken at noon on Oct. 29, 1948 in Donora, PA as deadly smog enveloped the town. 20 people were asphyxiated and more than 7,000 became seriously ill during this horrible event."
from: http://oceanservice.noaa.gov/education/kits/pollution/02history.html


from: http://www.eoearth.org/article/Donora,_Pennsylvania

"When Smoke Ran Like Water," a book about air pollution is among the books that you can check out, read, and report on to fulfill part of the writing requirements in this class (instead of doing an experiment report).  The author, Devra Davis, lived in Donora Pennsylvania at the time of the 1948 air pollution episode.